138 Papers from the Marine Biological Laboratory at Tortugas. 



(2) The calcareous remains of organisms living in the waters. 



(3) Detrital material washed behind the keys from the reefs and 



flats lying outside of them. 



(4) Some material may be brought southward along the west 



coast of Florida. 

 At present data are not available for determining the proportion due 

 to each one of these sources. 



GEOLOGIC DISTRIBUTION OF LIMESTONE IN FLORIDA. 



It may be appropriate here to give a statement of the geologic 

 history of limestone in Florida similar to that made for the siliceous 

 deposits. The following is a list of the calcareous formations of the State, 

 presented in stratigraphic sequence: 



Pleistocene: Palm Beach limestone, Miami oolite, Key Largo limestone, 



Key West oolite, Lostmans River limestone. 

 Pliocene: Marls are abundant but limestone is not known. 

 Miocene: Jacksonville formation : Contains some limestone beds. 

 Oligocene : 



Apalachicola group: Alum Bluff formation, some impure limestone; 



Chattahoochee formation, mostly impure limestone; Hawthorne 



formation, some limestone; Tampa formation, some limestone. 



Vicksburg group: This group is composed mostly of more or less pure 



limestone. There are some marl and sandy beds and layers of chert. 



In reviewing the geologic formation of Florida it is immediately 

 evident that the Vicksburg group comprises the great limestone forma- 

 tions of the State. Although there are calcareous constituents in the 

 Upper Oligocene, Miocene, and Pliocene, very rarely is there pure lime- 

 stone ; more frequently the material is composed of clays or sands with 

 a large proportion of calcareous matter. In other words, Florida is very 

 largely made up of continental waste, but the older geologic formations 

 contain sufficient lime to furnish calcareous material to the streams flow- 

 ing across their surface. 



TERTIARY CORAL REEFS OF THE SOUTHERN UNITED STATES. 



The role coral reefs have played in building up the Peninsula of 

 Florida can easily be understood by outlining the geologic history of the 

 reefs of that and adjacent regions as we now know them. 



Oligocene, Vicksburg Group. — There was no extensive development 

 of coral reefs during Vicksburgian time. In fact, the only reef known 

 which may be referable to it is the one at Salt Mountain, near Jackson, 

 Alabama. It is of comparatively few acres in extent, and regarded as a 

 constructive geologic factor is of almost negligible importance. 



Oligocene, Apalachicola Group. — Coral reefs belonging to this group 

 are known at several localities. Probably the most extensive develop- 

 ment is in the vicinity of Bainbridge, Georgia, where exposures may be 

 seen along Flint River from a point 3 or 4 miles below that town through 

 a distance of 4 or 5 miles. Reef corals of the same geologic age are also 

 known from the Mclntyre plantation, 11 miles south of Thomasville, and 

 at other places in Thomas County, Georgia; and from southern Lowndes 

 County. In Georgia, however, although there were Upper Oligocene 

 coral reefs they were not of great importance as constructional agents. 



